1. Field of the Invention
The present invention relates to a rotary table apparatus and an electric discharge machine having the same.
2. Description of the Related Art
As shown in FIG. 1, a bearing (not shown) is mounted in a rotary table apparatus 1 with reference to a rotary table casing 2, and a face plate 3 is mounted on an inner wheel of the bearing (not shown). The face plate 3 can freely rotate with respect to the rotary table casing 2. A cable-insertion hole 4 for driving a motor is formed in an upper surface (or side surface) of the rotary table casing 2. Joints 5 are mounted directly on the cable-insertion hole 4 to close the hole 4. Free tubes 6 are inserted into the joints 5 respectively. By inserting motor-driving cables (not shown) into the joints 5 and the free tubes 6, it is possible to supply motor-driving electric power to the rotary table apparatus 1 from outside thereof while keeping waterproof of the rotary table apparatus 1 (JP 2008-119793 A).
In an electric discharge machine shown in FIG. 2, the rotary table apparatus 1 is placed on a left work table 7 of a machining tank 20, and the free tubes 6 are placed along an edge of the machining tank 20. In this case, the free tubes 6 and a discharging cable 11 connected to an upper guide 10 do not come into contact with each other.
In an electric discharge machine shown in FIG. 3, the rotary table apparatus 1 is placed on a right work table 8 of the machining tank 20. In this case, since the joints 5 are oriented to a deep side of the machining tank 20, handling of the free tubes 6 become more complicated as compared with FIG. 2. Further, there is a possibility that the free tubes 6 come into contact with the discharging cable 11, the discharging cable 11 may be damaged or cut, and there is a high possibility that the rotary table apparatus 1 receives influence of noise during machining and discharging operations. If a configuration is changed such that the orientation of the joints 5 is rotated and the free tubes 6 are placed in front of the machining tank 20, contact with respect to the discharging cable can be avoided. However, to remove or detach the joints 5, a specialized tool is required in many cases, and if the joints 5 are erroneously fixed, waterproof of the joints 5 may be deteriorated. Therefore, this configuration is not preferable for a general operator.
Further, according to a configuration that the joint 5 is directly mounted on the rotary table casing 2 shown in FIG. 1, there is a problem that the cable-insertion hole 4 cannot be made greater than the joints 5 in size due to the structure of the joints 5. That is, when a connector mounted on a terminal of the motor-driving cable (not shown) is larger than the cable-insertion hole 4, since the cable cannot be inserted into the cable-insertion hole 4, it is necessary to mount the connector on the cable terminal after only the cable is inserted into the cable-insertion hole 4, and assembling efficiency of the rotary table apparatus 1 is poor.
If the joints 5 are made larger, this problem can be solved. However, since the free tubes 6 also become thick in proportion to the joints 5, costs of parts are increased. If the free tubes 6 are made extremely larger with respect to a diameter of the cables inserted into the free tubes 6, the cables rub in the free tubes 6 and may be damaged. Further, also when the rotary table apparatus 1 is fixed to a table in the machining tank 20, since the free tubes 6 are thick, handling thereof is deteriorated, and it becomes difficult to fix the rotary table apparatus 1 along the machining tank 20.